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CS1001 Lecture 27. Final Examination Review. From Before the Midterm. Basic Program Elements Declaration of Variables Declaration of Parameters Initialization of Variables Logical Operators Selective Execution CASE Statements Repetitive Execution How to Prompt for an Input. - PowerPoint PPT Presentation
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21 April, 2000
CS1001 Lecture 27
• Final Examination Review
21 April, 2000
From Before the Midterm
• Basic Program Elements• Declaration of Variables• Declaration of Parameters• Initialization of Variables• Logical Operators• Selective Execution• CASE Statements• Repetitive Execution• How to Prompt for an Input
21 April, 2000
Basic Program Elements
• Every program must have:– PROGRAM ProgramName– IMPLICIT NONE– END PROGRAM ProgramName
Declaration of Variables• REAL :: rVar1, rVar2• INTEGER :: iVar1, iVar2• CHARACTER(LEN) :: cVar1, cVar2*LEN• LOGICAL ::bVar
21 April, 2000
Declaration of Parameters
• REAL, PARAMETER :: rCONS = 3.14159• INTEGER, PARAMETER :: iCONS = 5240
Initialization of Variables• rVar1 = 1.23• iVar2 = 2240• cVar3 = “Hello world”• bVar4 = .TRUE.
21 April, 2000
Relational Operators
= =
/=
<=
>=
<
>
.EQ.
.NE.
.LE.
.GE.
.LT.
.GT.
Logical Operators
.NOT.
.AND.
.OR.
.EQV.
.NEQV.
Negation
Conjunction
Disjunction
Equivalence
Nonequivalence
21 April, 2000
Selective Execution
• Normal IF Structure• Simple IF Structure
• Normal IF StructureIF (log_exp1 .AND. log_exp2) THEN
statements to be performed
ELSE IF (log_ex3 .OR. log_ex4) THENstatements to be performed
ELSEstatements to be performed
END IF
21 April, 2000
Simple IF Statement
IF (logical_expression) stmt
e.g.,
IF (logical_expression) EXIT
Used to get out of an infinite DO loop
Equivalent to:
IF (logical_expression) THENEXIT
END IF
21 April, 2000
CASE Constructs
SELECT CASE (iItem)CASE (:0)
statements to perform if iItem <= 0
CASE (1)
statements to perform if iItem = 1
CASE (2:5)
statements to perform if iItem is 2-5
CASE (9:)
statements to perform if iItem >= 9
CASE DEFAULT
statements to perform for other values
END SELECT
21 April, 2000
Repetitive Execution
• Counter-controlled loops perform an operation a given number of times
• DO-EXIT or while or until loops perform an operation until a condition becomes true that causes the loop to end
• Counter-Controlled
DO iLoop = init_val, final_val, step_sizestatements to be performed
END DO
21 April, 2000
DO-EXIT (While) Loop
DO
statements to be performed
IF (logical expression) EXIT
statements to be performed
END DO
21 April, 2000
Prompting for Input
PRINT *, “Enter an integer from 1 to 9: ”
READ *, iInput
PRINT *, “Enter a value 0.0 or greater: ”
READ *, rInput
PRINT *, “Enter Q to quit: ”
READ *, cInput
21 April, 2000
Stuff Since the Midterm
• More Basic Program Elements
• Subprograms - Subroutines, Functions
• Structures
• One-Dimension Arrays
• Implied DO Loops
• Multi-Dimension Arrays
• Formatted Output
• Text Processing
• Internal Files
• How to Create a File
• How to Read from a File
21 April, 2000
More Basic Program Elements
• Programs containing subprograms must contain the following:
PROGRAM MyProgram
:
CONTAINS
subprograms go here (internal)
:
END PROGRAM MyProgram
subprograms go here (external)
21 April, 2000
Internal Subroutines
• Invoked with a CALL StatementCALL MySubRoutine(iArg, rArg)
• Defined after CONTAINS statementSUBROUTINE MySubRoutine(iArg, rArg)
INTEGER, INTENT(IN) :: iArg
REAL, INTENT(OUT) :: rArg
INTEGER :: iLocalVariable
REAL :: rLocalVariable
statements to be performed
END SUBROUTINE MySubRoutine
21 April, 2000
External Subroutines
• Invoked with a CALL StatementCALL MySubRoutine(iArg, rArg)
• Defined after END PROGRAM statementSUBROUTINE MySubRoutine(iArg, rArg)
INTEGER, INTENT(IN) :: iArg
REAL, INTENT(OUT) :: rArg
INTEGER :: iLocalVariable
REAL :: rLocalVariable
statements to be performed
END SUBROUTINE MySubRoutine
21 April, 2000
Internal Functions
• Invoked with an equation or statementrValue = rMyFunction(iValue)
• Defined after the CONTAINS statementFUNCTION rMyFunction(iValue)
REAL :: rMyFunction
INTEGER, INTENT(IN) :: iValue
statements to be performed
rMyFunction = some value to return
END FUNCTION rMyFunction
21 April, 2000
External Functions
• Invoked with an equation or statementrValue = rMyFunction(iValue)
• Declared as EXTERNALREAL, EXTERNAL :: rMyFunction
• Defined after the END PROGRAM statementFUNCTION rMyFunction(iValue)
REAL :: rMyFunction
INTEGER, INTENT(IN) :: iValue
statements to be performed
rMyFunction = some value to return
END FUNCTION rMyFunction
21 April, 2000
Structures (not in exam)• Declare a structure
TYPE sVariable
REAL :: rVar1, rVar2
INTEGER :: iVar1, iVar2
END TYPE sVariable
• Declare an instance of the structureTYPE(sVariable) :: sInstance
• Reference the variables in itiItem = sInstance%iVar1
rPrice = sInstance%rVar2
21 April, 2000
One-Dimension Array
• Declare and dimensionINTEGER, DIMENSION(1:9) :: iVar1, iVar2
REAL, DIMENSION(0:25) :: rVar1, rVar2
• Initialize whole arrayiVar1 = 0
iVar2 = (/ 1, 2, 3, 4, 5, 6, 7, 8, 9 /)
rVar1 = 9.99
rVar2 = (/1.0, 1.1, 1.2, 1.3, …, 1.25 /)
• Reference elements using subscriptiVar(8) = 25
rVar(19) = 17.49
21 April, 2000
Multi-Dimension Array
• Declare and dimensionINTEGER,DIMENSION(1:9,1:3):: iVar1, iVar2
REAL, DIMENSION(0:25,1:5) :: rVar1, rVar2
• Initialize whole arrayiVar1 = 0
rVar1 = 9.99
• Reference elements using subscriptiVar(8,2) = 25
rVar(19,5) = 17.49
21 April, 2000
Formatted Output
PRINT 20, iVar, rVar, cVar
20 FORMAT(1X, I2.2, 5X, F8.3, T20, A)• 1X, 5X - horizontal spaces
• I2.2 - Integer, width of 2, minimum 2 digits
• F8.3 - Real, width of 8 (including sign and decimal point), with 3 decimal places
• T20 - Tab to absolute column position - column 20
• A - Alphabetic string
21 April, 2000
Creating a File
• The file is opened as a new file for writingOPEN(UNIT=12, FILE=“input.dat”, “NEW”, “WRITE”)
• Formatted data is written to the fileWRITE(12,40) iVar, rVar, cVar
40 FORMAT(1X, I5, F8.3, A25)
• The file is closedCLOSE(12)
21 April, 2000
Reading from a File
• The file is opened as an old file for readOPEN(UNIT=13, FILE=“input.dat”, “OLD”, “READ”)
• Formatted data is read from the fileREAD(13,40,IOSTAT=EOF) iVar, rVar, cVar
40 FORMAT(1X, I5, F8.3, A25)
• The file is closed– CLOSE(13)
21 April, 2000
Internal Files
• Used to convert character form to integergiven cDate = “November 25,1997”
then cYear = cDate(14:17)
and READ (UNIT = cYear, FMT = ‘(I4)’) iYear
• Assigns the integer value 1997 to integer variable iYear
21 April, 2000
Text Processing
• Getting the length of a stringVar = LEN(String)
Var = LEN(“Hello, my name is”) => 17
• Finding text within a stringFound = INDEX(String, Text)
Found = INDEX(“IMAGINE”, “IN”) => 5
21 April, 2000
Implied DO Loops
• Used to read data into an arrayREAD (10, *) (iInArr(I), I=1, iLastNum)
• Equivalent toDO I = 1, iLastNum
READ (10, *) iInArr(I)
END DO
